INSIGHT SEAT POST EXTENDER 22.2MM THE SEAT POST EXTENDER IS MADE FOR RACERS WHEN YOU NEED TO WARM UP OR COOL DOWN AFTER A RACE, OR FOR WHEN YOU WANT A MORE COMFORTABLE SITTING POSITION WHEN CRUSIING AROUND, DUE TO THE ULTRA LOW FRAME DESIGNS AND SUPER SHORT RACE SEAT POSTS. You just insert your current seat post and seat into the externder and ride away. * The Insight Seat Post extender requires a 2nd seat clamp to clamp down the post into the extender. Round seat tube sizes : 22.2mm. INSIGHT seat post extender 22.2 x 360mm black - Uses 25.4 seat Clamp. Round seat tube sizes : 25.4mm. INSIGHT seat post extender 25.4 x 420mm black - Uses 31.8 seat Clamp. Round seat tube sizes : 26.8mm. INSIGHT seat post extender 26.8 x 420mm black - Uses 31.8 seat Clamp.